In a mobile communication system, the propagation environment varies under the influence of fading. Therefore, it is necessary to transmit a signal in accordance with the propagation environment.
As means for controlling a transmission signal, techniques such as adaptive modulation and coding (AMC), transmit power control (TPC) and the like have been used.
The adaptive modulation and coding is transmission signal control means for adaptively controlling the modulation scheme and the code rate which are optimum for a mobile communication terminal apparatus. Further, the transmit power control is transmission signal control means for controlling the transmission power of the transmission signal of a mobile communication terminal.
In the adaptive modulation and coding and the transmit power control, the modulation scheme, the code rate, or the transmission power is controlled such that the optimum transmission signal can be transmitted based on the quality of a reception signal (hereinafter referred to as “the reception quality”). Accordingly, it is necessary to estimate the reception quality at the receiver apparatus.
Patent Literatures 1 and 2 each disclose technique of measuring, as the reception quality, a desired signal to interference signal ratio (hereinafter referred to as “the SIR (Signal to Interference power Ratio)”) from the desired signal level (hereinafter referred to as “the RSSI (Received Signal Strength Indicator)”) and the interference signal level (hereinafter referred to as “the ISSI (Interference Signal Strength Indicator)”) of a reception signal.